The invention relates to glass fiber-reinforced thermoplastic compositions; in particular, the invention relates to compositions containing grafted acrylate rubber and polyamide that are suitable for molding articles having good surface quality.
A glass fiber reinforced thermoplastic molding composition suitable for the preparation of articles having good surface properties is disclosed.
The composition contains a resinous blend and a filler component. The resinous blend contains (i) 20 to 50 wt. % of a grafted acrylate rubber, (ii) 2 to 10 wt. % of a first copolymer containing structural units derived from styrene (meth)acrylonitrile and maleic anhydride, (iii) 20 to 80 wt. % polyamide, and (iv) 0 to 40 wt. % of a second copolymer containing structural units derived from styrene and (meth)acrylonitrile, the percents being relative to the total amount of (i), (ii), (iii) and (iv). The filler component of the inventive composition contains 5 to 50 percent of milled glass fibers, the percent being relative to the weight of the molding composition. Optionally, the inventive composition also contains a positive amount of a wollastonite. Molded articles that are prepared of the composition feature good mechanical properties and excellent surface quality.
The thermoplastic molding composition of the present invention contains a resinous blend and a filler component. The resinous blend contains
(i) 20 to 50, preferably 25 to 45 percent by weight of a grafted acrylate rubber (herein referred to as ASA),
(ii) 2 to 10, preferably 4 to 8 percent by weight of a first copolymer having a weight average molecular weight of 60,000 to 180,000, preferably 100,000 to 140,000 g/mole and containing structural units derived from styrene (including substituted styrene wherein substituents are halogens or alkyl groups, as well as alpha methyl styrene), (meth)acrylonitrile and maleic anhydride, and
(iii) 20 to 80, preferably 25 to 60 percent by weight of polyamide.
(iv) 0 to 40, preferably 5 to 25 percent by weight of a second copolymer having a weight average molecular weight of 70,000 to 200,000, preferably 105,000 to 155,000 g/mole, the structure of which contains units derived solely from styrene and (meth)acrylonitrile.
The filler component of the inventive composition contains 5 to 50, preferably 20 to 40 percent of milled glass fibers having an average length of about {fraction (1/64)}xe2x80x3 to {fraction (1/16)}xe2x80x3, said percent being relative to the weight of the molding composition.
Optionally, the inventive composition may further contain a positive amount of up to 25 percent by weight, preferably up to 22 percent (relative to the weight of the molding composition) of wollastonite, in the form of particles having an average length of 20 to 300, preferably 40 to 200 microns and particle diameter of 2 to 20, preferably 3 to 10 microns.
The ASA Resin
Component (a), the ASA resin (acrylate-styrene-acrylonitrile interpolymer), is known as an impact-modified, substantially thermoplastic resin which comprises a SAN matrix in which is dispersed an acrylate elastomer phase as impact modifier. Advantageous ASA resins which are commercially available comprise a crosslinked (meth)acrylate elastomer, a crosslinked SAN copolymer and a substantially linear SAN copolymer. Methylated styrenes such as xcex1-methyl styrene or vinyl toluene may be used in place of all or part of the styrene.
The ASA resins may be prepared by a variety of known methods involving emulsion or bulk polymerization. The preferred ASA resins are of core-shell structure; these structures are well known in the art and have been disclosed in, among others U.S. Pat. No. 3,944,631 that is incorporated herein by reference. The (meth)acrylate elastomer core portion of these resins may be composed of alkyl, aryl, or arylalkyl esters of acrylic or methacrylic acids. These may be prepared by a two-step process in which the (meth)acrylate elastomer core (which may by at least partially crosslinked, such as by the known incorporation of polyfunctional vinyl compounds) is covered with a thermoplastic shell of polymethyl methacrylate, polystyrene, styrene-acrylonitrile copolymer, or similar vinyl (co)polymers.
Other ASA resins which may be advantageously used in the composition of the invention are the types disclosed in U.S. Pat. Nos. 3,655,824; 3,830,878; 3,991,009; 4,433,102; 4,442,263; and 4,409,363, all of which are incorporated herein by reference. These ASA resins are thermoplastic resins that are typically made of an acrylate ester, styrene (or xcex1-methylstyrene), and acrylonitrile. These resins exhibit good impact, heat distortion and weathering characteristics.
The ASA component of the inventive composition is present in an amount of 20 to 50, preferably 25 to 45 percent by weight relative to the weight of the resinous blend.
The First Copolymer
The first copolymer, having weight average molecular weight of 60,000 to 180,000, preferably 100,000 to 140,000 g/mole, contains structural units derived from styrene (including substituted (xcex1-methyl)styrene wherein substituents are halogens or alkyl groups), (meth)acrylonitrile and maleic anhydride.
Structurally, the first copolymer contain 50 to 90, preferably 60 to 80 wt. percent of units derived from styrene, 10 to 50, preferably 20 to 40 wt. percent of units derived from (meth)acrylonitrile and 0.2 to 30, preferably 0.5 to 5 wt. percent of units derived from maleic anhydride, the wt. percents being relative to the weight amount of the named structural components of the first copolymer. The preparation of the first copolymer is conventional.
The first copolymer is present in the inventive composition in an amount of 2 to 10, preferably 4 to 8 percent by weight relative to the weight of the resinous blend.
The Polyamide Resin
The polyamide resins used in the blends of this invention are well known in the art and embrace semi-crystalline and amorphous resins having a molecular weight of at least 5000 and commonly referred to as nylons. Suitable polyamides include those described in U.S. Pat. Nos. 2,071,250; 2,071,251; 2,130,523; 2,130,948; 2,241,322; 2,312,966; 2,512,606; 3,393,210; 2,071,250; 2,071,251; 2,130,523; 2,130,948; 2,241,322; 2,312,966; and 2,512,606; all incorporated herein by reference.
The polyamide resin may be produced by condensation of equimolar amounts of a saturated dicarboxylic acid containing from 4 to 12 carbon atoms with a diamine, in which the diamine contains from 4 to 14 carbon atoms. Excess diamine can be employed to provide an excess of amine end groups over carboxyl end groups in the polyamide. Examples of polyamides include polyhexamethylene adipamide (66 nylon), polyhexamethylene azelaamide (69 nylon), polyhexamethylene sebacamide (610 nylon), and polyhexamethylene dodecanoamide (612 nylon), the polyamide produced by ring opening of lactams, i.e., polycaprolactam, polylauric lactam, poly-11-amino-undecanoic acid, bis(paraaminocyclohexyl) methane dodecanoamide. It is also possible to use in this invention polyamides prepared by the copolymerization of two of the above polymers or terpolymerization of the above polymers on their components, e.g., an adipic, isophthalic acid hexamethylene diamine copolymer. Preferably, the polyamides are linear with a melting point in excess of 200 degree xc2x0C. The term xe2x80x9cnylonxe2x80x9d as used herein refers to nylon containing conventional compounding ingredients as are known to those skilled in the art. Examples of the polyamide resin are Nylon 4, Nylon 6, Nylon 7, Nylon 8, Nylon 9, Nylon 11, Nylon 12, Nylon 66, Nylon 610, etc. These polyamide resins may be used alone or in combination.
The polyamide component of the inventive composition is present in an amount of 20 to 80, preferably 25 to 60 percent relative to the weight of the resinous blend.
The Second Copolymer
The second copolymer, having weight average molecular weight of 70,000 to 200,000, preferably 105,000 to 155,000 g/mole, the structure of which contains units derived solely from styrene and (meth)acrylonitrile wherein the structural units derived from styrene amount to about 55 to 85% and the units derived from acrylonitrile amount to 15 to 45%, the percents being relative to the total weight of the named structural components of the second copolymer. The preparation of the second copolymer is conventional.
The second copolymer is present in the inventive composition in an amount of 0 to 40, preferably 5 to 25 percent by weight relative to the weight of the resinous blend.
The Filler Component
The filler component is present in the inventive composition in an amount of 5 to 50, preferably 20 to 40 percent relative to the weight of the molding composition. The filler is essentially milled glass fibers, that is glass fibers having an average length of about {fraction (1/64)}xe2x80x3 to {fraction (1/16)}xe2x80x3. In an additional embodiment of the invention the filler is a mixture of milled glass fibers with wollastonite.
Milled Glass Fibers
Milled glass fibers have been widely used as a filler for polymeric systems, see, for instance, U.S. Pat. Nos. 4,381,352, 4,680,214, and 4,861,803. The standard milled glass fiber used in the industry has a diameter of about 16 micrometers and average length of about {fraction (1/64)}xe2x80x3 to {fraction (1/16)}xe2x80x3. More information relative to the milled glass fibers has been disclosed in S. H. Metzger, Jr. and K. Seel, xe2x80x9cHigh Modulus RIM Elastomers for Automotive Extedor Body Panelsxe2x80x9d in J. Cell. Plastics, 268-273 (1981) and in U.S. Pat. No. 4,381,352, both incorporated herein by reference. The length of a glass fiber can be expressed in various ways, such as average fiber length or as bulk density. For example, the average length of a xe2x80x9c{fraction (1/16)}-inchxe2x80x9d milled glass fiber is about 0.006 inches (0.253 mm) and the bulk density of such a fiber is about 0.500 g/cm3. It has now been found that milled glass fiber, having a diameter of 10 to 20 micrometers provides unexpected advantages when used as a filler for the inventive composition.
The inventive composition contains 5 to 50, preferably 20 to 40 percent of milled glass fibers the percent being relative to the weight of the molding composition.
The Optional Component
Characterized in terms of the physical dimensions of its particles, the median diameter (D50) of the optional wollastonite component in the context of the present invention is about 2 to 20, preferably 3 to 10, most preferably 4 to 10 microns and its length is about 20 to 300, preferably 30 to 250, most preferably 40 to 200 microns. The median diameter of the wollastonite, is determined as equivalent spherical diameter by Sedigraph (X-ray). The length (volume-weighted mean) is determined microscopically by image analysis. The amount of the optional wollastonite in the inventive composition is a positive amount of up to 25 percent, preferably up to 22 percent (the percents being relative to the weight of the molding composition).
Other additives known in the art for their art recognized function may also be included in the inventive composition in functional amounts. These include flame retarding agents, mold release agents, lubricants and stabilizers, including thermal, hydrolytic and UV stabilizers as well as dyes and pigments.
The inventive composition offers distinct advantages over corresponding compositions that contain chopped glass fibers or wollastonite or a combination of chopped glass fibers and wollastonite. The surface properties of the instant compositions are surprisingly and unexpectedly improved there over.
The preparation of the inventive composition is conventional and may be carried out by following procedures and using equipment that are well known to the art-skilled.
The invention will be better understood with reference to the following examples, which are presented for purposes of illustration rather than for limitation, and which set forth the best mode contemplated for carrying out the invention.